1. Field of the Invention
The present invention relates to a dust-proof mechanism for an image scanner, and more particularly to a dust-proof mechanism for optical reflection module of the image scanner.
2. Description of the Prior Art
In an image scanner, the scanned light beam is reflected by an optical reflection module arranged in the scanner to form an image through an optical lens. Typically, a Charge Coupling Device (CCD) is used to convert the optical signal of the image into digital signal which can be memorized and processed by a computer. In a commercial scanner product, due to the limitation of the length of the optical path required in forming the image, generally the optical reflection module includes several reflection mirrors (for example, three or four glass mirrors) for several times reflecting the light beam so as to effectively reduce the dimension of the scanner.
FIG. 1 shows a conventional image scanner including a housing 1 and an upper cover board 2. The scanner comprises a light transmittable document positioning plate 11 which is a plane surface made of for example glass or other light transmittable, substantially rigid material, for supporting a document to be scanned (not shown), defining a document scanning widow.
FIG. 2 shows the arrangement of the internal components of the conventional image scanner. The housing 1 encloses circuit components, optical components and mechanical components of the scanner, including two parallel guide rods 31, 32, a first optical reflection module 4, a second optical reflection module 5, an optical lens 6, and a Charge Coupling Device 7. The first and second optical reflection modules 4 and 5 are driven by a driving mechanism and transmission mechanism, such as a belt, to slide along the guide rods 31, 32 so as to control the optical path during scanning operation.
The first optical reflection module 4 includes a module frame 40 and an upper and a lower reflection mirrors 41, 42 arranged in the module frame 40. The two reflection mirrors are arranged opposite to each other to contain an angle for reflecting the light beam. The front side of the optical reflection module frame 40 facing the second optical reflection module 5 is formed with an open area.
After a long period of operation of the scanner, it often takes place that suspending dust attaches to the mirror surface of the optical reflection module, especially in an optical reflection module frame with open area. The lower mirrors 42 of the first optical reflection module 4 is such arranged that the mirror surface is oriented upward, so that the suspending dust is most apt to attach to the mirror surface thereof. Once the dust attaches to the surface, a problem of poor scanned image will take place. For example, straight stripes will be formed on the image. In order to achieve a best quality of the scanned image, it is necessary to provide a dust-proof mechanism so as to isolate or reduce the suspending dust attaching to the mirror surface.